Electromagnetic circuit breaker having a solenoid with a hydraulic time delay means



Feb. 8, 1966 R. B. HEILMAN 3,234,344

ELECTROMAGNETIC CIRCUIT BREAKER HAVING A SOLENOID I WITH A HYDRAULICTIME DELAY MEANS Filed Jan. 18, 1963 4 Sheets-Sheet 2 H9 IO! 93 nh i mll4 INVENTOR.

RAYMOND B.HEILMF\N 5 QT TOR J Feb. 8, 1966 R. B. HEILMAN 3,234,344

ELECTROMAGNETIC CIRCUIT BREAKER HAVING A SOLENOID WITH A HYDRAULIC TIMEDELAY MEANS Filed Jan. 18, 1963 4 Sheets-Sheet 5 WELD SUSPENSONsTRUCTURE. O BROKEN nwr-w HERE AND PQQT'LY OMFFTED FOR CLRQlTY INVENTOR.RAYMOND B. HEILMAM irrpmw R. BIHEILMAN 3,234,344 ELECTROMAGNETIC CIRCUITBREAKER HAVING A SOLENOID Feb. 8, 1966 WITH A HYDRAULIC TIME DELAY MEANS4 Sheets-Sheet 4.

Filed Jan. 18, 1963 INVENTOR. BY RAvM'omo B. HEILMHM /415 HTTOQ/UE JUnited States Patent )flFice 3,234,344 Patented Feb. 8, I966 3,234,344ELECTROMAGNETIC CIRCUIT BREAKER HAV- ING A SOLENOID WITH A HYDRAULICTIME DELAY MEANS Raymond B. Heilrnan, Trenton, N.J., 'assignor toHeinemann Electric Company, Trenton, N.J., a corporation of New JerseyFiled Jan. 18, 1963, Ser. No. 252,404 17 Claims. (Cl. 200-97) Thisinvention relates to the electromagnet of a magnetic circuit breaker ofthe type in which the contacts open after a time delay period forcertain overloads and instantaneously at higher overloads and, moreparticularly, to an improved movable tube of an electromagnetic devicefor controlling the variation in the time delay period for a givenoverload as the ambient temperature changes between extreme limits. Thisinvention also relates to an arrangement for automatically resetting themovable tube duringthe opening of the contacts after electromagneticopening of the contacts either instantaneously or after a time delay.

A fully electromagnetic circuit breaker of the time delay type isillustrated by Wilckens Patent No. 2,360,922, in which a movablemagnetic core is housed within a stationary nonmagnetic tube and thecore is moved by certain overload currents from one end of the tubetoward the other end to increase the strength of the magnetic field andto trip open the circuit breaker contacts after a time delay byactuating a pivotal armature. Movement of the core in such circuitbreakers is retarded by a spring and the dash pot action of a siliconeoil, both within the tube, the oil during the movement of the coremoving from one side of the core to the other in the annular orificedefined by the clearance between the core and the tube. Due to thechange in volume and viscosity of the oil as the temperature changes,the time delay period produced by such an arrangement varies somewhatwith the temperature of the oil, resulting in the electromagnetictripping of the circuit breaker after time delay periods which vary, tosome degree, for the same overload current as the temperature varies.

While it is true that use of silicone oils has been preferred because,among other reasons, the viscosity of silicone oils changes little withtemperature changes, a characteristic which is relatively well known,(Chambers Technical Dictionary, Third Edition, 1958, p. 1013), in someuses it is desirable to compensate for even this small change inviscosity because of the variation in time delay periods which it wouldotherwise produce, so as to reduce the variation in time delay periodsfor the same overload current conditions, as the temperature changesgreatly, i.e., compensate for temperature changes.

Also, in prior arrangements, an air bubble in the tube housing themagnetic core and the silicone oil has been used to accommodate thevolume changes of the oil as the ambient temperature varies. But the airbubble tends to resist being split in its passage from one side of thecore to the other, which may impede the core travel in excessof what isdesired, or if the air bubble manages somehow to move from one side ofthe core to the other,

as one unit, the core would be impeded less than usual during suchmovement, and in either case a variable volume of the space housing thefluid automatically varies in direct response to the pressure exerted bythe fluid on the walls enclosing it. The preferred fluid is a liquid inthe operating temperature range, and since the volume and the viscosityof a liquid are interrelated, compensation for the varying viscosity isachieved by using the change in fluid volume, and the consequent changein pressure on the walls enclosing it, to move the initial position ofthe core and also simultaneously change the size of the orifice throughwhich the fluid must flow during movement of the core, to compensate forthe fluids ditferent viscosity at the different temperature.

In view of the foregoing, it is, therefore, an object of this inventionto provide an improved tube for the electromagnet which automaticallyprovides some compensation for varying ambient temperatures so as toresult in a time delay period, at certain overloads, within apredetermined range.

In this invention the tube itself is attracted toward the coil toinitiate movement of the mechanism to the conacts open position, atcertain overloads after a time delay period and at higher overloadsinstantaneously, and, hence, another object of this invention is toprovide an arrangement which uses a part of the linkage mechanism(during its movement to the contacts open position) to reset the tube toits initial position automatically and simultaneously with opening ofthe contacts.

In one embodiment of the invention the electromagnet comprises a coilwhich surrounds, in part, a movable tube formed of nonmagnetic materialexcept for a tube end cap or pole and a movable core within the tube.The interior of the tube is divided into two spaces by a flexible,expansible member or bellows, the movable mag netic core being disposedin one of the spaces in which is also a fluid whose volume and viscosityvaries with temperature. The movable core divides the space containingthe fluid into two smaller spaces and movement of the core toward thecoil (and the tube magnetic cap or pole) is retarded by a spring and thedash pot action of the fluid which passes through orifices'from theunderside of the core to the upper side thereof. The expansion andcontraction of the fluid, due to the arrangement of the various parts,varies the size of one of the orifices as the temperature varies andalso varies the initial position of the core (relative to the coil), tocompensate, to some degree, for the changes in temperature of the fluidand the tube so as to control the variation in time delays, as thetemperature varies, for a given overload current within the range ofcurrents in which a time delay is desired.

The foregoing and other objects of the invention, and the best mode inwhich I have contemplated applying such principles will more fullyappear from the following description and accompanying drawings inillustration thereof.

In the drawings,

FIG. 1 is a sectional view, partly in elevation, of a circuit breakerembodying the present invention, illustrating the contacts openposition;

FIG. 2 is an enlarged sectional View of the movable tube illustrated inFIG. 1, showing the internal details thereof for the contacts openposition and the normal temperature;

FIG. 3 is a sectional view taken along the line 3--3 in FIG. 1 but partof the suspension structure for the movable tube has been broken awayfor illustrative purposes and the mechanism is illustrated in the tripfree position;

FIG. 4 is a partial view taken along the line 44 in FIG. 3 but in FIG, 4some of the suspension structure 3 for the movable tube is illustratedwhich is not illustrated in FIG. 3;

FIG. 5 is a fragmentary diagrammatic view showing the contacts in theopen position and illustrating primarily the movable contact armengaging the tube reset spring for automatically resetting the movabletube when the contact arrn moves toward the open position; 7

FIG. 6 is an end elevation view taken along the line 6-6 in FIG. 5; and

FIG. 7 is a view similar to FIG. 5 but illustrating the contacts in theclosed position and the movable contact arm disengaged from the tubereset spring to allow the tube to move down during electromagnetictripping.

Referring to the drawings, there is illustrated-a circuit breaker 10,including an outercasell and terminal structures 12 and 13 extendingtherefrom. The terminal structure 12 is connected within the case by aconductor 14 to a coil 15 forming part of 'an electromagnet 15 which, onpredetermined overload current cond'itions, moves axially a tube 20,thelatter being partly of magnetic material and functioning in themanner of an armature for the solenoid coil 15. The tube. 20 controls 'alinkage mechanism 21 of the circuit breaker for auto matically (onpredetermined overload conditions) opening the contacts 22 and 23 bypivoting the contact22 out of engagement with the stationary contact 23.For opening the contacts, the movable contact 22is carried by a movablecontact arm 24 pivoted at the'right on'laterallyprojecting feet 25, thearm'24 being electrically connected by a flexible conductor 19 tothecoil 15. Manual opening and closing of the contacts 22 and .23 isefifectuated by a handle '28, whereas electromagnetic tripping of thecontacts to the open position is efiectua'ted by the pivotal movement ofa lock 29 (FIG. 4) upon suitable downward movement of the tube 29 andpivoting of-the counterweight suspension structure 30 (FIGS. 3 an Thelinkage mechanism 2 1;comprises two groups of links referred tofor'convenience as the handle toggleor first group 3i and the maintoggle or second group 32. The linkage is more fully described andclaimed in a copending patent application filed onDecember 24, 1962, byRaymond B. Hellman and Harold H. Bahr, Serial No. 246,699.

Briefly, however, pivotal counterclockwise movement of the handle. 28,starting from the open contacts position of FIG. 1, causes the handle.toggle links 31 comprising the handle link 33 and a link of varyinglength 34 (joined together by a knee-pintle 42) to move to the right andthe handle force to be transmitted ,by a coupling link 35, from the linkof varying length 34 to the knee pintle 41 of the main toggle 32, thelatter" comprising the toggle links 37 and 38,;and the catch link 391$The lower link 38 is, in; turn, connected to the movable contact arm 24,whereby movement of the handle link 33 results in the movable arm 24being rotated in counterclockwise direction, closingthe contacts 22 and23. 'In the closed position of the contacts, thecatchlink 39 isrestrained from movementby a lock 44. carried by a cradle 45. In turn,the cradle 45 is restrained by the lock 29 from moving in thecounterclockwiseidirection (due to the bias imposed on the cradle 45 bythe catch link 39) from the force of the openingfsp'rings 48.

When the tube 20 moves downwardlya sufficient distance, uponpredetermined overloads, the tube 20 pivots clockwise (FIGS. 1 and 4)thecounterwe'ight suspension structure 30 sufiiciently to engagethe lock'29 and rotate the latter in the clockwise "direction falso. Suflicientclockwise rotation of the lock 29 results in the release of the cradle45, whereby they catch link 39 is released and-the'upper end of thecatch link 39'moves in the clockwiseidirection under; the bias of theopening springs ls. This'clockwise movement of the catch link 39 causesthe toggle formed by links 37 and 38 to collapse to the left (FIG. 1);due to the pressure of the openin g springs 48, whereupon thecontactsopen. 'Dur-' ing the collapse of the main toggle links, the kneepintle 42 of the handle toggle is moved overcenter (toward the left)sulficiently for the spring 51 (carried by the link of varying length34) to help reset the mechanism.

Referring to FIG. 2, the tube 20 comprises a generally cylindrical case55 of nonmagnetic material, preferably stainless steel, definingxashoulder 56, which divides the case 55 into'a lower case part 57 ofsmaller diameter than the upper case part 58. The lower case part 57 isclosed and completely 'sealedby a nose (cap or pole) piece 60, ofmagnetic material, welded to the. case part 57 and having an axialopening through which extends an elongated pin 62 of nonmagneticmaterial, also preferably of stainless steel and welded to the lower endof the nose 60 (to completely seal the tube). The upper end of the tube20 is closed byv acap 63, of non-magnetic material and preferably ofstainless steel, and welded to the upper case part 58 and a bellows 65to seal a space 66;. v

. The interior of the tube 20 is divided by the expansible, flexiblemember or bellows 65 into the first space 66, completelyv filled ,with'a fluid, and a. second space '67, thebellows being formed of a thinmetallic material and preferably from nickeL. The first space 66comprises an i lower partefi, an intermediate .part 69; (between theshoulder 56 and the lower end ofthebellows 65) and an upper annular part7tl circumferentially surrounding the space 67. Disposed within theintermediate space 69 and extending into the lower space at all times,asufficientdistance 10 be surrounded in part at all times by the coil 15and its magnetic-frame 7 0, is a movable core or armature 72 of magneticmaterial and comprising an elongated annular lower tube 73 and anintegral annular upper piston 74. v i e v Z The core 72 moves aiallyrelative to the tubular case 55 of the tube 20, and is guided insuch movement by the sliding 'fitbetweenthe annular tube 73 and theinner surface of the tubular case part 57 and the. sliding fit betweenthe pistonjfl and the inner surface of the upper tubular case part 58,the latter two jointly defining an annular orifice 75. The piston 74carries and has attached in spacedrelation thereto, preferably by spotweld ing, an orifice plate 76 housing a floating annular orifice valve86, the plate 76 havinga centrally formed orifice 77 and massive 835 anorifice 187 for. jointly with a metering pin 80, controlling the rate offluid flow between 0pposite sides of the piston 74 during axial,downward movement of'the core 72.

The metering pin 80 for the orifice 87 depends from and is securedto alower plate 79 secured to and car,- ried by the bellows 65, the orificeplate 76 being biased by a core spring 81 toward the bellows plate 79 atall times. The core spring "81 is seated at its lower end a ainst themagnetic nese 50, extends into the axial opening 820i thecore72, and isseated at the up'pe'r end against a shoulder 83 formed on 'thecore 72,the spring 81 resisting downward movement of the core and returningit toits initial position after electromagnetic tripping. Afterelectromagnetic tripping, the fioatingannular valve 86 provides for thefast return of the fluid into the space69. e r V I The metering pinj80is concentric with the upper portion of the pin '62, the metering pin 80being provided with a longitudinal openingsfs into which the pin 62slid'ably'fits for 'g uiding' the metering pin 8% during movement of thelatter. As illustrated, the core spring 8 1is also concentric with thepins 62' and '80 and with the lower portion of the core 72 and "thespring 81 'is inter mediate the Stland, the core 72.

The bellows plate 79 is biased downwardly at all times against thejfluidwithin the space 66 by 'an axial sprin g88centr'ally positioned withinthe bellows'65. A threaded hole 90 is provided in the cap '63 to receivea threaded plug 96 which bears against the upper end of the spring "88inthereby adjust, within certain limits, the force exerted downwardly bythe spring 88 on the bellows plate 79 and the fluid.

To limit upward travel of the core 72 and properly:

J seal the space 66, the upper end of the case part 58 has an innersurface which defines two annular shoulders 92 and 93 separated by acylindrical wall 94. A cylindrical sleeve 95, concentric with the uppertubular case part 58, interfits with and abuts, a portion of the innersurface of the case part 58 and has an upper bent rim 97 lying upon theshoulder 92, as illustrated in FIG. 2, the lowermost terminal portion 98of the sleeve 95 acting as a stop to limit upward movement of the core72 by abutment therewith of the upper periphery of the orifice plate 76.

The bellows 65 is generally of cylindrical shape with a closed, lower,horizontal end to which the plate 79 is secured and which defines withthe length-wise convolutions a cylindrical space of variable volume, asdetermined by the volume of the fluid within the space 66, the bellows65 being of one piece construction.

The bellows 65 has an upper, flexible end portion 99 which extend-supwardly between two hollow (for flexibility), stainless steel rings 101and 4102, each of one piece construction. The cap 63 is provided withtwo shoulders 1108 and M9, the vertical surface of shoulder 108 biasingthe ring 192 radially outward against the bellows end portion 99, thelatter being urged against the ring 101, which is in turn urged againstthe inside of the uppercase '8. Vertically upward movement of the ring102 is restrained by the horizontal surface of shoulder 108 and downwardmovement by the outwardly rolled edge portion .105 which forms anannular lip-like ledge, as illustrated in FIG. 2, below a horizontalplane through the center of the ring 102. The horizontal surface of theshoulder 109 biases another part of the bellows end 99, downwardlyagainst the ring 1111, after the bellows end has been turned atapproximately a 90 angle, as illustrated in FIG. 2, while downwardmovement of the ring 101 is prevented by the rim 97.

The bellows end '99 then extends horizontally beyond the ring 101 andlies between the shoulder 93 and the horizontal surface of shoulder 109,the bellows end 99 being then again turned at 90 angle to extendupwardly between the rim of the cap 63 and the rim of the upper casepart 58. An interference fit is provided between the cap 63, the bellowsend 99, and the inner rim surface (119 of the upper case part 58 and thecap is pressed into position to preliminarily seal the space 66. Thefinal step in sealing the space 66 is to weld the extremity of bellowsend 99 annularly with a bead type weld to the outer periphery of the cap63 and the upper case part 58, as illustrated.

The coil .15 is formed by a suitable number of turns of wireelectrically insulated from each other and wound upon a non-magneticmetal tube 111. The magnetic frame 70 for the coil is provided by anopen ended almost completely annular tube, of L-shape in crosssection,except for the slot 114 (FIG. 2). That is, the frame 70 includes anintegral top wall with an opening to receive the case part 57 and theframe extends down around the coil 15. The top, horizontal wall of theframe 70 has an annular lip 118, as best illustrated in FIG. 2, whichstands up with a thickness approximately the same as that of the piston74 of the core 72, to aid in completing the magnetic circuit when thetube and core 72 are in their lowermost positions.

The bottom of the coil 15 is closed by a magnetic pole or bushing 115which also extends within the cylindrical space defined by thenonmagnetic tube 111 about which the coil is wound. The pole 115, FIG.1, is of L-shape in cro-sssection, ends slightly above the middle of thelength of the tube 111, has a slot (not shown) extending axiallysimilarly to slot 11-2, and the pole 1115 closes the bottom of the coil,except for a radial continuation (of the aforementioned slot) throughwhich the flexible conductor v19 extends. The tubular part of thebushing 115, adjacent its juncture with the horizontal part of thebushing 115, FIG. 2, is formed on its outside surface,

6 i.e.', facing the coil, with an annular, undercut, half-moon shapedrecess 117. The presence of the bushing with the undercut recess .117extending into the cylindrical space defined by the tube 111, asdescribed, was found to significantly raise the overload current valueat which instantaneous overload tripping took place.

Secured to the pole '115 is a bearing'116 through which extends thelower part of the pin 62 for guiding the tube 20 during movement and forlimiting upward movement of the tube 20 by engagement of the reset plate142 with the bearing 116.

The nose 60 and pin 62 interfit with the pole piece 115,

as illustrated, to define an air gap Z of variable size dependent on theaxial position of the tube 20 and an annular space between the nose 60and the pole piece 115 of constant radial size regardless of the axialposition of the tube. Similarly, the piston 74 (of the core 72) over::lies the top surface of the frame 70 to define an air gap between thelatter and the lower surface of the piston 74 of varying size dependenton the axial position of the tube 20 and an annular space between thetube 73 and the coil 15 of constant radial size regardles of the axialposition of the tube 20.

The counterweight suspension structure '30 (FIGS. 3 and 4) is formed byspaced plates and 121 which are pivoted intermediate their ends onpintles 122 (FIG. 4) secured to arms 1123, the latter being welded attheir right hand ends to the frame plates .124 of the mechanism. Thespaced plates 120 and 121 are also pivotally connected by pintles 126 tothe tube 20, the pintles 126 being secured to the right of pintles 122and to the tube 20 by a strap which frictionally and tightly engages theouter surface of the tube 20 and is carried thereby. Springs 128 areprovided to bias the pintles 126 above or below the pintles r122, thesprings .128 having their right hand ends connected to the counterweightplates 120 and 121 between pintles 123 and .126. The counterweightstructure 30 is further described and claimed in a separate patentapplication filed January 18, 1963, by Ronald Nicol, Serial No. 252,413.

As illustrated in FIGS. 1 and 5 to 7, coiled about a pin 14!) (securedto the spaced frame plates 124) is a reset torsion spring 141 for thetube 20. The reset spring 141 has one end secured to-a reset plate 142which is in turn secured to the lower end of pin 62 of the tube 20. Theother end of the reset spring 141 is disposed to the left of anextension 1 43, the latter being secured to the right hand portion ofthe arm 24, FIGS. 5 and 7, and having a lateral portion 144. Theextension 143 and the associated end of the reset spring 14 1 arearranged relative to each other so that in the closed position of thecontacts, FIG. 7, the lateral portion 144 is spaced from the near end ofreset spring 141, the spring 141 being relaxed at this time and appliesno bias to the tube 20. When the mechanism moves from the contactsclosed to the contacts open position, whether by manual movement of thehandle 28 or electrom'agnetica-lly by release of the cradle 45 (by thepivotal lock 29), the lateral portion 144 engages the associated end ofthe spring 141 and depresses it, causing the other end of the resetspring 141 to exert a force upwardly upon the pin 62 of the tube (20which is suflicient, upon denergization of the coil 15 (that is,extinction of any are that may form) to reset the tube 20 by moving itupwardly sufiiciently for the pintles 126 (of the counterweightstructure 30) to move above the center of pintles 122, at which time thesuspension springs 128 also help to move the tube 20 up to its reset oropen contacts position.

When the mechanism is in the contacts open position, as illustrated inFIG. 1, manual closing of the contacts is accomplished by manuallymoving the handle 28 counterclockwise about the pintle 152 of the handlelink 33. This movement of the handle 28 forces the handle toggle kneepintle 42 to move the sliding link down against the upward of the handletoggle spring '51 (the latter being carried-by the L-shaped link 1'54which pivots about pin'tle1153) and further compresses theIspiringSL'moving thepin'tlef42 from theleft of a centerj lineconnectingthe pintles ,152 and .153, towardthe rig t hereer; TheL shaped'link 'isalso connected to link "33 byfloating link 148 through I pintles 42 and155 and the L-shaped link 154 carries'the pintle1155 about .thefpint1e1j3 in a manner to maintain the 'floating'link :148 and thec'oupling link35 in force transmitting relation and 'the'L-shaped link 154 performsthis-same function during, electromagnetic tripping, Continuedcounterclockwise movement of the handle 28 causestheknee pintle 4Q.tornove through the center line between the "pintles 1'52 and 1'53 andto the right hand side'thereof, the line of action'of the handle togglespring" 511 now moving-from theletttothe right o tthe linebetween'pintles 152*and '153, whereby the toggle spring il'now movesjthehandle toggle links to the rightfwith a snapact-io'n, until the handlelink 33 abuts against the rightst op pin.15=7, FIG. 'l,thehandle togglespring'51 remaining jmorecompre'ssed when the handle'link as abutstheright 'stop in 157 than when it abuts theleftsto'p pin lSS. v V

When the linkage is turned to thefclosed pbsitionfof the contacts,thetogglelinks37 and 38Lgo"overcenter to the right andthespring'force"of'the' opning springs 48 tend to rotate the catch link'39 clockwise, but rotation of the catch link is restrained'by thelocklip 44 carried by the cradle'45. I t I Atpredetermined'ciirrentconditionsfabove a current level at which insta'ntaneous'tripping of thecircuit breaker is desired the electromagnetic flux is sufficient aboutthe magnetic nose 6t) andma'gneticc'orefl to create a pull on the tube20 whichmovesit sutficiently downwardly, to pivot the "counterweightstructure 30 v and the lock 29 (including'thelattersfinturnedl1atcl1'160, ElG. 3) out of engagemenfiwith the, upperend of. the cradle 45 at'which'tim'e the catch .link.39'isfreleased bythe lock lip 44. The toggle -for'rned by links '37 and 38 nowcollapsesto'the'left' and the movable 'a'rmf24moves to its contactsopen. position under the bias'o fthe openingispri'ngs' 48. and a contactfo'rce spring 162, FIG. 1. Upon the occurrence "of ove'rlo'ad'currentsabove a certain percentage in excess of the 1 rated load but below theaforementioned higher, instantaneous trip current value, the'tube '20provides time"delays'between 'the occurrence ofjthe'overlo'ad'current'andj the opening of the contacts, These time delays varyi'forthe Shine overload current value depending ion thetemperature'oftheitube20 but the variation due to temperature changes is rereduced, i.e.,"compensated, by the arrangement of the tube20.

That is, when thejcoilflS is energized, a' magnetic field isestablihejdin themag netic frame 70am about the :ma'gneticfnose 6 0 andthe j'rnagnetic movable core 72. The-magnetic field'is insufficient,'at'rated'loajd condi- 20 againstthe upward fo'rcepla'ced'on'theltubeZO-by the counterweight "structure "30 or to move the core towardthecoil1'5fagainst the retarding springfil'and' fluid within space '65.However, upon the occurrence of overload-currents above acertainpercentage inexeess of the rated current but below theaforementioned'higher, in-

s'tant'a'neous trip current, this magnetic field does sufficientlyattract the armature 7 2 to' start movementf thereoftowardthe coil 15,,against the'bias ofth'e core spring 81 and'the'dampingetfect of'thefluid within the space 66 'such time against plate 76. As the magnetic:core 72 moves downwardly toward the coil, the magnetic force ,on'thecore 72 and'on the magnetic nose idilincreases,

due to thefactthat the reluctanceof the circuit'is being lowered, sincethe equal gaps, indicated as X and Win FIG. 2, arebeing decreased. Whenthe core movesdownwardly sufliciently, that is, as the piston 74approaches or contacts the shoulder 56 and the lower end of the coretube extension 73 approaches or contacts the nose '69, the magneticforce on the magnetic nose 60 becomes great enough to overcome theupward force of the counterweight structure 36 and the magnetic forcenow moves the entire tube 20 through the equal gap distances, indicatedas Y and Z, in FIG. 2, between the shoulder 56 and the top of themagnetic frame 70, and between the nos'e'dtl and the lower pole 115.This movement of the tube 20 carries with it the arm 165 of thecounterweight structure 30 which strikes the pivotal lock 29 topivot-the latter sufficiently to release the cradle 4-5 andthere'byrelease the catch link 39, whereby the main toggle links 37 and38 collapse to move the arm 24 to the open contacts position. v v

When'the counterweight structure 30 so'rnoves, once the pintle 126 ofthe counterweight'structure passes below the horizontaljplane throughthe center of pintles 122, the spring 128 of the counterweight structure30 also helps to move the time delay tube device 2t) downwardly with asnap action, since the spring 128 now biases the pintle126 downwardlyalso.

' The closer the current values approach the instantaneous'trip value,the faster will the core 72 'move toward the coil 15, because thestrength of the magnetic field is then'greater and this will in turnincrease the magnetic 'fieldso as to achieve a force on the magneticnose 60 which is sutficient to move the tube 2t) downwardly-without theneed for the movable core to move through any or all of the entire gapdistances, labeled X and Win FIG. 2. Thus, an inverse time delayresults, that is, long time delays at smaller overloads and shorter timedelays at largeroverloads. Upon the occurrence of short circuits orextremely 'high'o'verloads above the instantaneous trip current value,the tube 20 moves downwardly without any movement of the core 72. Thatis, the current at such times creates a sufficiently high magnetic pullon the magnetic nose 60 to, with the aid of the force on the fluid dueto the pullon the magnetic core 72, instantaneously move the tube 2.6downwardly for instantaneously tripping open the circuit breaker.

The movable core 72, the fluid completely filling the space66, and'thebellows '65 are arranged so that the piston 74 is at the predetermineddistance X above the shoulder 56 at the normal ambient temperature of 75F .,'this dimension being checked after assembly of the tube 20 byX-rays (but before welding together the cap 63, the case rim 119, andthe bellows end 99). If necessary'the tube is disassembled and refilledto insure'that 'the amount of fluid, and, hence, the volume of the space66, is the amount required to result in the predetermined distance X,within the tolerancedesired.

When the ambient tem perature varies from 75 F., the volume of the fluidwithin the space fiechanges and the viscosity of the fluid also changes.I

The metering pin has an outside surface to-cornpensate'fortheternperature changes, the pin outside surface comprising threestepped tapers and a cylindrical portion at the lower end, of a diameterlarger than any of the tapered surfaces, the smallest tapered diameterbeing at theend of thepin 80 attached to the'bellows 65 and the largestdiameter at the opposite end, as illustrated 'in FIG. 2. Upward movementof the core 72 is stopped by the lower end 98 of the aluminum slecve' ata predetermined temperature but it should be noted that at temperaturesabove, this predetermined temperature the -bellows may continue tocontract, to a position deter- "mined by'the springs 88 and 170, movingthe pin 80 upwardly, even though further movement of the core 72 isprevented. Contraction of the bellows 65 is at all times initiallyresisted by the spring 88, but to further resist the upward force on thebellows 65 (exerted by the fluid) the second spring 170 is placed withinthe first spring 88 (seated upon the bottom of the bellows andengageable with the plug 96), the second spring 170 being of shorteraxiallength than the first spring and coming into action only after thebellows 65 has contracted an amount equal to the difference between thelength of the two springs 88 and 170.

Thus, assuming the existence of the normal temperature of 75 F. and anoverload current in the range to produce a time delay before the openingof the contacts, the movable core 72 will move downwardly and the fluidwill flow upwardly through the orifices 75 and 87. The orifice 75 is offixed size but the orifice 87 varies in size as the core 72 movesbecoming smaller as the core 72 moves down until the piston 74 abuts theshoulder 56 after it has travelled through the distance X, FIG. 2.

But when the temperature of the fluid increases above the, normaltemperature, the volume of the fluid increases and its viscositydecreases, contracting bellows 65, and the metering pin 80 and the core72 move upward. Upon an overload current within the time delay rangesuflicient to initiate downward movement of the core 72, the fluid flowsupwardly through the orifices 75 and 87. The orifice 87 is of the samesize, initially as during the position ofthe core 72 for the 75 F.normal temperature up tothe aforementioned higher predeterminedtemperature but above this predetermined temperature the orifice 87 issmaller, due to the fact that upward movement of the core 72 has stoppedbut not that of the pin 80. At temperatures above 75 F., when the core72 has moved through a distance equal to the distance X for the normal75 F. temperature, the size of the opening between the orifice 87 andthe pin 80 decreases from the size existing at the end of travel of thecore 72 at the normal temperature. Such reduction in size jointly withthe longer distance through which the core 72 must travel at theincreased temperature, compensates for the decreased viscosity toprovide a time delay, at temperatures above the normal temperature,which approximates the time delay period at the normal temperature for agiven overload, in the range of overload values where a time delay isdesired.

When the ambient temperature decreases from a temperature above 75 F. tothe normal 75 value, the fluid in the space 66 and the force of thesprings 88 and 170 return the metering pin 80, the bellows 65, and themovable core 72 to the normal 75 F. position, as illustrated in FIG. 2.

If the ambient temperature drops below 75 F., the

fluid decreases in volume and increases in viscosity and the core 72moves (at the decreased temperature) relative to the metering pin 80less than at the normal 75 F. temperature because contraction of thefluid causes the bellows 65 to elongate and moves the core 72 down(against the force of spring 31) to an initial position closer to thenose 60 than the normal position of the core 72 at the normaltemperature. Also, elongation of the bellows 65 under pressure of spring88, as the fluid contracts, results in lowering of the pin 80 so that asmaller outside surface diameter defines with the valve 86 a largerorifice 87 during the end of the down ward travel of the core 72 so thatultimately a larger orifice 87 exists (after-the core 72 moves its fullamount) than exists "at the end of core travel at the normaltemperature, thus compensating for the increased viscosity .of the fluidat lower temperature.

normal, a larger orifice 87 resultsbetween the metering pin 80 and thevalve 86 (relative to the opening at the normal temperature) for thefluid to flow through, because the lower temperature contracts the fluidcausing the bellows to expand, thereby lowering the pin and the core 72,this larger opening resulting at the time movement of the core 72 endsduring a time delay period. Similarly, when the fluid temperatureincreases from normal, at the end of core travel, a smaller orifice 87will result between the pin 80 and the valve 86 because the highertemperature expands the fluid (against the springs within the bellows)raising the pin 80 and the core 72.

Thus, it is seen that when the fluid temperature decreases and itsviscosity increases, since the orifice 87 is larger and the travel ofcore 72 toward nose 60 is less, time delay compensation has been madefor the increased fluid viscosity for overloads in the time delay range.Similarly when the fluid temperature increases and its viscositydecreases, since orifice 87 is now smaller and the travel of core 72toward the nose 60 is longer, time delay compensation has been made forthe decreased fluid viscosity for overloads in the time delay range.

The method used to exclude all of the air from the space 66 when fillingit with silicone oil is described hereinafter. Initially the variousparts are preconditioned by immersing them in a beaker containingsilicone oil and heating them for about one hour at about 400 F., in anassembly chamber by heat from the electrical heating coil of theassembly fixture to be used subsequently in the assembly of the tube.Thereafter, the air is evacuated by the use of suitable pumps from theassembly chamber.

The pumping continues until bubbling activity from the assembly chambersubs-ides to a low rate at which time the assembly chamber is returnedgradually to atmospheric pressure and room temperature. Subsequently theassembly chamber is again evacuated and this process is repeated untilno bubbles are observed at temperatures of about 400 F. Allof themoisture and some of the absorbed gases in the silicone oil and metalparts are removed by this alternating procedure of heating and pumping.

The first step is to immerse the case 55 completely in a suitablequantity of silicone oil contained in an assembly fixture (notillustrated) which is placed within the assembly chamber. The corespring 81, the core 72 including its valve 87 and plate 76, the sleeve95, the ring 101, and the bellows 65 are then submerged in the sillconeoil, in almost the desired final axial position relative to the case 55,and aligned, at such time, by a guide sleeve wall forming part of theassembly fixture. At this time some of the silicone oil is displacedinto the reservoir forming part of the assembly fixture. (The guidesleeve wall is concentric with the case 55 and forms an axialcontinuation of the cylindrical wall 94.) This placement of the parts inthe case 55 is accomplished within the assembly chamber at a vacuumpressure of about 2 millimeters (mm.) of mercury and at a temperature ofabout 400 F. produced by the electrical heating coil forming part of theassembly fixture. During this operation the space 67 (enclosed by thebellows 65) becomes filled with silicone oil also.

The second step is commenced at a temperature of about 400 F. and avacuum pressure of 2 mm. of mercury or less. When a satisfactory levelof evacuation. is achieved, evidenced by only an occasional smallbubble, the temperature is reduced to about 300 F. With the space 66sealed jointly by the bellows end 99, the ring 101, the guide wall and apositioning sleeve having a circular surface for holding firmly thebellows end 99 against the upper surface of the ring 101, air atatmospheric pressure is allowed to return at a slow rate into theassembly chamber. Entrance of such atmospheric air tends to furtherinsure that the bellows 65 will be firmly seated against the siliconeoil in the space 66 with no air bubble between the two. Thereafter, theassembly chamber is returned to a vacuum pressure of 2 mm. or less andthe temperature is stabilized at about 300 F. At such time the ring 101,the sleeve 95, the core 72 and the bellows 65 are jointly moveddownwardly by a press which forcefully moves'downwardly and positionsthe sleeve rim 97 '(of sleeve '95,.) against the shoulder 92, i.e., thefinal desired position illustrated in FIG, 2. During such movement tothe final position, some of the silicone oil between the bellows '65 andthe case 55 is displaced through a small port in the guide sleeve intothe reservoir, further insuring the complete filling of the space d6.Also, a plunger is placed within the bellows 6'5 to resist the tendencyof the bellows to compress, while it is moved downwardly against thesilicone oil;

The bellows 65 is made so that at the temperature of 300 F, the bellowsis neither extended nor compressed bythe siliconeoilwithinthe space66.This neutral position was selected for the filling of the space "66 toavoid the use 'of devices to extend or contract the bellows tocorrespond to its length at some other temperature.

The third step is commenced with the fixture and the tube at about 300F., the assembly-chamber being gradually brought to atmospheric pressureand the guide sleeve and positioning sleeve are thereafter removed. The'fluid which has entered the "space 67 is also removed at this timefa'ndthe springs 88 and 170, the ring sea, the cap 63 and the plug% areplaced in approximately the correct axial position. The assembly chamberis then reclosed and brought to a temperature of about 125 F. and avacuum pressure of about 10 mm. of mercury. The cap 63 and the ring 102are then forcefully driven by the press until the ring 102 is just pastthe center of the ringf101, to the position illustrated in FIG. 2.

Simultaneously, the cap 63 is pressed into position against the bellowsend 99 and Within the rim 119 to jointly seal the space '65 due to theinterference fit therebetween. Thereafter, the tube 2t) is removed fromthe assembly chamber and the weld about the cap 63, the

'bellows end 99 and the rim 119 is madeto'permanently insure the sealforthe space 66. t

4 Thus, no air is allowed into the space 66 which couldaccomrn'ddateexpansion and contraction of the silicone oil and "all suchexpansion and contraction is reflected in afchangedlength of the bellows65.

Hence, a tube has been provided in which only the core and the nose areof magnetic material, the rernainde r being -of non-magnetic materials,functioning in "the nature of an armature 'for the coil and providinginstantaneous tripping at certain overloads and timedelay tripping atother overloads. Further, the positions of thecore and the metering pinchange, as the temperature changes, so that the time delay will approachthe time delay at the normal temperature for the same current value. I p

Also, a small quantity of the same kind of silicone oil as is placed inthe space 66 maybe placed in the space '57 so that when the temperatureincreases sufiiciently to vaporize thesilicone oil in the space 67 thedownward force on the bellows 65 is sufiiciently in excess of the upward"forceon the bellows -65 to maintain the latter in contact with thesilicone oil in the space '66, miniinizing the "tendency or the siliconeoil within the space 156 to vaporze and maintaining any vaporization ofit toja minimum. Further, to create such a vapor force within thespace67, the threaded connection between the plug 96 and the cap :63 ishermetically sealed, such as, referring to FIG. 2, by circuniferentiallybrazing the joint between the plug and the cap at the junction of theupper horizontal surface of the cap 63 and the threaded portionof-th'e'plug 96.

axially extending portion extending less than half way within the tubeof nonmagnetic material, a second tube movable from a first position toa second position upon predetermined overload current conditions, saidsecond tube being surrounded partially by said first tube and said coil,said second tube including a forward end cap of magnetic materialsurrounded at least in part at all times by said first tube and coil, abearing secured to said frame for positioning said second tube relativeto said frame and coil, a bellows within said second tube for dividingsaid tube into first and second spaces, a fluid of varying voiume as thetemperature changes within said first space, a movable core of magneticmaterial within said first space, a spring for biasing said movable coreagainst said bellows, said movable core being partly surrounded by saidframe and coil and partly outside of said frame and coil, said movablecore being movable from a first positionspaced from said frame to asecond position closer to said frame against the bias of said spring,whereby upon a changein temperature, the volume of said first spacechanges and the position' o f said movable core changes also due to itsbeing biased against said bellows, whereupon subsequent predeterminedoverload current conditions the electromagnetic flux causes said movablecore to move through a distance that is variable depending on thetemperature.

t 2. The structure recited in claim 1 wherein said fluid also varies inviscosity as the temperature varies, said movable core forms an orificefor the flow of fluid therethrough upon movement of said core bytheelectromagneti'c flux, said movable core divides said first spaceinto two portions between which said fluid flows through said orifice, apin carried by said bellows and within said orifice, said pin having anouter surface of 'varyingshape to variably restrict said orifice, theposition of said pin relative to said orifice being dependent on thevolumeof said first space, whereby the pin compensates 'for changes inviscosity of the fluid by variably restricting the orifice. 3. In acircuit breaker having a linkage controlling separable contacts, anelectromagnet for providing an inverse time delay period relative to themagnitude of the overload current for overloads above a firstpredetermined current and below a second predetermined currentcomprising the combination or a tube movable from a first position to asecond position by electromagne'tic flux, movement of said tube towardsaid second position initiating separation of said contacts, a coil,said tube being surrounded in part by said coil, said tube comprising aflexible member separating the interior of the tube into first andsecond spaces, the first space being filled with a fluid which varies involume and viscosity dependent upon the temperature, a movable core ofmagnetic material within saidfi'rst space, a spring withinthe secondspace biasing said flexible member against the mass of fluid in saidfirst space, a second spring for biasing said movable core intoengagement with said flexible member, said movable core subdividing saidfirst space into a first portion and a second portion,saicl movable corehaving an orifice for placing said first and second space portions incommunication Witheach other, and said flexible member carrying ametering pin extending into said orifice, whereby at predeterminedoverload currents after suflicient movement of said tube during a timedelay period from said first position toward said second positionseparation of said contacts is initiated by the linkage of the circuitbreaker, the aforesaid structure controlling the variation in the timedelay period as the temperature of thefluid changes.

4.1m a circuit breaker, the combination comprising an electromagnetincluding a coil, a hollowtube of nonmagnetic material movable from afirst position to a second position, said coil surrounding and'slidablyreceiving a portion of said tube, the portion of said tube surrounded bysaid coil including an end cap of magnetic material, an expansiblemember within said "tube dividing the interior of the tube into a firstspace and a second space, a movable core of magnetic material withinsaid first space, said first space containing a liquid whose volume andviscosity varies with temperature, said movable core being operativelyconnected to said expansi-ble member for controlling the axial positionof said core relative to said coil as the temperature varies, said corebeing spaced from said end cap of said tube to form a gap andmovabletoward said end cap upon predetermined current conditions by theelectromagnetic flux of the coil, whereupon suflicient movement of saidcore .and reduction of the gap, the magnetomotive force on the end'capincreases suific'iently to move the tube toward its second position; 5.In a circuit breaker having a pair of separable comtacts, anelectromagnet for providing an inverse time delayrelativeto themagnitude of the overload current including a'coil mounted upon a tubeof nonmagnetic materiaL-a. magnetic frame for said coil and a secondtube movable from a first position to a second position uponpredetermined overload to open said contacts, the improvement in saidsecond tube comprising a bellows dividing said second tube into firstand second spaces, a fluid in said first space of varying volume andviscosity as the temperature of the second tube changes, a movablearmature core of magnetic material in said first space, said first spacebeing completely filled with fluid to substantially exclude all air,said second space being defined by the volume enclosed by said bellows,said movable core being biased against said bellows so that as thevolume of the fluid in the first space changes, the volume of thebellows changes and the position of the core relative to the coil andthe magnetic field produced by the latter changes, said core includingan orifice for the flow of fluid therethrough and from one side to theother of said core when said core is attracted toward said coil toprovide a retarding dash pot action, a metering pin carried by saidbellows, associated with said orifice, and variably positioned relativethereto thereby, upon temperature changes, to vary the size of theorifice, to decrease the orifice size upon increases in temperature ofthe second tube and to increase the orifice size upon decreases intemperature of the second tube.

6. The structure recited in claim wherein said second tube has a portionof magnetic material in the magnetic field of said coil, and saidmetering pin has an annular surface shape of varying diameter along itslength, the end of said metering pin of smallest outside diameter beingoperatively connected to said bellows and the end of said metering pinof largest outside diameter being at the end of said pin toward whichsaid core moves when attracted by the magnetic field of said coil.

7. In a circuit breaker having a pair of separable contacts, anelectromagnetic device for providing an inverse time delay relative tothe magnitude of the overload currents, said electromagnetic deviceincluding a coil energized by said overload currents, and a tube movabletoward said coil to electromagnetically initiate separation of thecontacts, the improvement in said tube comprising an expansible memberwithin said tube forming with a part thereof a space of variable volume,a liquid within said space completely filling said space, a magneticmovable core within said space, a spring biasing said magnetic core toone end of said space, said magnetic core defining an orifice, ametering pin for variably restricting said orifice and controlled bysaid expansible member in response to changes in volume of said liquidto increase the orifice restriction as the liquid expands and decreasesthe orifice restriction as it contracts.

8. The structure recited in claim 7 wherein said magnetic core is biasedagainst said expansible member, said core being disposed between saidcoil and said expansible member so that as the liquid expands themagnetic core is moved away from the coil and as the liquid contractsthe magnetic core is moved closer to the coil.

9. The structure recited in claim 8 wherein said tube is formed in partof magnetic material between the core and the coil.

10. In a circuit breaker having a pair of separable contacts, anelectromagnetic device for providing an inverse time delay relative tothe magnitude of the overload currents in a predetermined range ofoverload currents, said electromagnetic device including a coilenergized by said overload currents and a tube movable toward said coilto electromagnetically initiate separation of contacts, the improvementin said tube comprising expansible and contractable wall structureforming a space of variable size, a liquid substantially filling saidspace and excluding sufficient air therefrom so as to prevent thepresence of an air bubble which would tend to accommodate the changes involume of the liquid, a movable core of magnetic material also withinsaid space and attractable toward said coil during said predeterminedrange of overload current values, said liquid retarding the movement ofsaid core at such times, whereby as the volume of said liquid varies asthe temperature varies, said wall structure automatically defines aspace of different size, and movement of the core is retarded only bythe liquid and is not affected by an air bubble.

11. The structure recited in claim 10 and further including a variablyrestricted orifice carried by said core, the restriction of said orificebeing controlled by said wall structure in response to the volumechanges of said liquid.

12. The structure recited in claim 11 wherein the core is biased towardthe portion of the wall structure at the end of the space away from thecoil, said space being expansible in the direction away from said coiland contractable in the direction toward said coil, so that as theliquid expands the core is moved away from the coil and as the liquidcontracts the core is moved closer to the coil.

13. The structure recited in claim 12 wherein the tube is formed in partof magnetic material between the core and the coil.

14. In a circuit breaker, the combination comprising an electromagnetincluding a coil, a hollow tube of nonmagnetizable material movable froma first position to a second position relative to said coil, said coilsurrounding said tube in part, the part of said tube surrounded by saidcoil including a magnetizable pole piece, a movable core of magnetizablematerial within said tube, a spring biasing said core away from saidpole piece, a fluid within said tube for retarding movement of saidcore, said tube being movable toward said pole piece upon predeterminedoverload currents to decrease the magnetic reluctance of the magneticcircuit established by said coil about said pole piece and core andthereby increase the magnetic pull on the pole piece of said tubesufiiciently to move said tube from said first to said second tubeposition after a time delay, the magnetic pull on said pole piece athigher, predetermined overload currents being sufficient toinstantaneously move the tube from the first to the second tubeposition.

15. In a circuit breaker, an electromagnetic comprising the combinationof a coil, a frame of magnetic material for said coil, a cylindricalspace defined by said coil, a tube partially extending into said spaceand movable from a first to a second position, said frame including amagnetizable bushing extending into said space on the side opposite saidtube, said bushing having an undercut annular surface facing said coil,said tube including a pole piece of magnetic material in interfittingrelation with said bushing but spaced therefrom to establish an air gapof variable size axially and an annular space of constant radial sizebut variable in axial position, a movable core of magnetizable materialwithin said tube, said core being partially disposed in the cylindricalspace defined by said coil and partially outside thereof and overlappinga portion of said frame to establish with said frameia second air gapofvariable size and with said'tube pole piecea third air gap of-variablesizeand'a second annular space of constant radial size but of variableaxial position;

16. In a circuit breaker, an electromagnet comprising acoil defining-acylindrical space, a tube'partially extending-into said-space andmovable from a first position to a second posit-ion, a'flexible memberdividing the tube interior;- into-two spaces, oneoi said spaces beingfilled with a fluid that varies in volume and viscosity as itstemperature changes, a movable core of'magnetic material in the.space'filled withthe-fluid and-attractable by the magnetic: field ofsaid-:coil, said coreincluding an orifice for the: flow therethroughofsaid fluid upon movement of the core; and a metering pin variablypositionable by the flexible member as the flexible member expands andcontracts in response :to the change invoiu-me of the fluid, said :pincooperating with said orificeto restrict the orifice as' thetemperatureof the' fluid increases and to enlarge the orifice asthetemperaturedecreases, saidv core. being movable by themagnetic field of the coilbetween a first and a second position, and movement of. the-core towardsaidsecond position during predetermined over:

load currents thereafter movingflhe tubeaft ir. ll? dl'ty- References.Citedhyzthe Examiner UNITED; STATES" PATENTS B-ERNARD A. GILHEANY;Primary- Examiner.

ROBERT K. SCH'AEFER, Examiner.

1. IN A CIRCUIT BREAKER, AN ELECTROMAGNET FOR PROVIDING AN INVERSE TIMEDELAY RELATIVE TO THE MAGNITUDE OF THE OVERLOAD CURRENT COMPRISING THECOMBINATION OF A TUBE OF NONMAGNETIC MATERIAL, A COIL MOUNTED UPON SAIDTUBE, A TUBULAR FRAME OF MAGNETIC MATERIAL CIRCUMFERENTIALLY PARTIALLYSURROUNDING SAID COIL, SAID FRAME EXTENDING AXIALLY THE LENGTH OF SAIDCOIL AND INCLUDING END COVERS OVERLYING THE ENDS OF SAID COIL AND ANINTERNAL AXIALLY EXTENDING PORTION EXTENDING LESS THAN HALF WAY WITHINTHE TUBE OF NONMAGNETIC MATERIAL, A SECOND TUBE MOVABLE FROM A FIRSTPOSITION TO A SECOND POSITION UPON PREDETERMINED OVERLOAD CURRENTCONDITIONS, SAID SECOND TUBE BEING SURROUNDED PARTIALLY BY SAID FIRSTTUBE AND SAID COIL, SAID SECOND TUBE INCLUDING A FORWARD END CAP OFMAGNETIC MATERIAL SURROUNDED AT LEAST IN PART AT ALL TIMES BY SAID FIRSTTUBE AND COIL, A BEARING SECURED TO SAID FRAME FOR POSITIONING SAIDSECOND TUBE RELATIVE TO SAID FRAME AND COIL, A BELLOWS WITHIN SAIDSECOND TUBE FOR DIVIDING SAID TUBE INTO SAID FIRST AND SECOND SPACES, AFLUID OF VARYING VOLUME AS THE TEMPERATURE CHANGES WITHIN SAID FIRSTSPACE, A MOVABLE CORE OF MAGNETIC MATERIAL WITHIN SAID FIRST SPACE, ASPRING FOR BIASING SAID MOVABLE CORE AGAINST SAID BELLOWS, SAID MOVABLECORE BEING PARTLY SURROUNDED BY SAID FRAME AND COIL AND PARTLY OUTSIDEOF SAID FRAME AND COIL, SAID MOVABLE CORE BEING MOVABLE FROM A FIRSTPOSITION SPACED FROM SAID FRAME TO A SECOND POSITION CLOSER TO SAIDFRAME AGAINST THE BIAS OF SAID SPRING, WHEREBY UPON A CHANGE INTEMPERATURE, THE VOLUME OF SAID FIRST SPACE CHANGES AND THE POSITION OFSAID MOVABLE CORE CHANGES ALSO DUE TO ITS BEING BIASED AGAINST SAIDBELLOWS, WHEREUPON SUBSEQUENT PREDETERMINED OVERLOAD CURRENT CONDITIONSTHE ELECTROMAGNETIC FLUX CAUSES SAID MOVABLE CORE TO MOVE THROUGH ADISTANCE THAT IS VARIABLE DEPENDING ON THE TEMPERATURE.